New isoniazid/ethionamide resistance gene mutation and screening for multidrug-resistant Mycobacterium tuberculosis strains

QSAR based therapeutic management of M. tuberculosis

Mycobacterium tuberculosis is responsible for severe mortality and morbidity worldwide but, under-developed and developing countries are more prone to infection. In search of effective and wide-spectrum anti-tubercular agents, interdisciplinary approaches are being explored. Of the several approaches used, computer based quantitative structure activity relationship (QSAR) have gained momentum. Structure-based drug design and discovery implies a combined knowledge of accurate prediction of ligand poses with the good prediction and interpretation of statistically validated models derived from the 3D-QSAR approach. The validated models are generally used to screen a small combinatorial library of potential synthetic candidates to identify hits which further subjected to docking to filter out compounds as novel potential emerging drug molecules to address multidrug-resistant tuberculosis. Several newer models are integrated to QSAR methods which include different types of chemical and biological data, and simultaneous prediction of pharmacological activities including toxicities and/or other safety profiles to get new compounds with desired activity. In the process, several newer molecules have been identified which are now being assessed for their clinical efficacy. Present review deals with the advances made in the field highlighting overall future prospects of the development of anti-tuberculosis drugs.

Resistance to Isoniazid and Ethionamide in Mycobacterium tuberculosis: Genes, Mutations, and Causalities

Isoniazid (INH) is the cornerstone of tuberculosis (TB) chemotherapy, used for both treatment and prophylaxis of TB. The antimycobacterial activity of INH was discovered in 1952, and almost as soon as its activity was published, the first INH-resistant Mycobacterium tuberculosis strains were reported. INH and its structural analog and second-line anti-TB drug ethionamide (ETH) are pro-drugs. INH is activated by the catalase-peroxidase KatG, while ETH is activated by the monooxygenase EthA. The resulting active species reacts with NAD+ to form an INH-NAD or ETH-NAD adduct, which inhibits the enoyl ACP reductase InhA, leading to mycolic acid biosynthesis inhibition and mycobacterial cell death. The major mechanism of INH resistance is mutation in katG, encoding the activator of INH. One specific KatG variant, S315T, is found in 94% of INH-resistant clinical isolates. The second mechanism of INH resistance is a mutation in the promoter region of inhA (c-15t), which results in inhA overexpression and leads to titration of the drug. Mutations in the inhA open reading frame and promoter region are also the major mechanism of resistance to ETH, found more often in ETH-resistant clinical isolates than mutations in the activator of ETH. Other mechanisms of resistance to INH and ETH include expression changes of the drugs' activators, redox alteration, drug inactivation, and efflux pump activation. In this article, we describe each known mechanism of resistance to INH and ETH and its importance in M. tuberculosis clinical isolates.

Molecular analysis of isoniazid and rifampin resistance in Mycobacterium tuberculosis isolates recovered from Barcelona

We studied the presence of mutations in the whole katG gene and specific regions of the oxyR-ahpC and mabA-inhA regulatory region in 61 Mycobacterium tuberculosis isoniazid-resistant isolates. An 81-bp region of the rpoB gene was also sequenced in 17 rifampin-resistant strains. Alterations in the katG gene were detected in 55% of the isolates. Mutation in codon 315 was the most prevalent (32%). Strains showed a high level of resistance, and most maintained a substantial catalase-peroxidase activity. Three strains with an isoniazid MIC of >or=32 microg/ml lacked catalase-peroxidase activity. Two of them had deletions in the catalytic domain of the KatG protein. One strain with deletion and three strains with mutations in the C-terminal domain showed low-level resistance and conserved the catalase-peroxidase activity. Mutations in the mabA-inhA regulatory region were identified in 32% of the isolates. All had low-level resistance, and the vast majority conserved catalase-peroxidase activity. Seventeen percent of the isoniazid-resistant isolates had no detectable alterations at the studied loci. Resistance to rifampin was associated with mutations in the 81-bp of the rpoB gene in all cases. IS6110 analysis indicated that recent transmission contributed substantially to the emergence of isoniazid- resistant tuberculosis in Barcelona through short transmission chains. A rapid genotypic assay, including the 315-katG codon and the -15 nucleotide of the mabA-inhA regulatory region, may cover 62% of isoniazid- resistant strains in Barcelona. In contrast, the targeting of the 81-bp region of rpoB would detect all our rifampin-resistant isolates.

In vitro inhibition of the Mycobacterium tuberculosis beta-ketoacyl-acyl carrier protein reductase MabA by isoniazid

The first-line specific antituberculous drug isoniazid inhibits the fatty acid elongation system (FAS) FAS-II involved in the biosynthesis of mycolic acids, which are major lipids of the mycobacterial envelope. The MabA protein that catalyzes the second step of the FAS-II elongation cycle is structurally and functionally related to the in vivo target of isoniazid, InhA, an NADH-dependent enoyl-acyl carrier protein reductase. The present work shows that the NADPH-dependent beta-ketoacyl reduction activity of MabA is efficiently inhibited by isoniazid in vitro by a mechanism similar to that by which isoniazid inhibits InhA activity. It involves the formation of a covalent adduct between Mn(III)-activated isoniazid and the MabA cofactor. Liquid chromatography-mass spectrometry analyses revealed that the isonicotinoyl-NADP adduct has multiple chemical forms in dynamic equilibrium. Both kinetic experiments with isolated forms and purification of the enzyme-ligand complex strongly suggested that the molecules active against MabA activity are the oxidized derivative and a major cyclic form. Spectrofluorimetry showed that the adduct binds to the MabA active site. Modeling of the MabA-adduct complex predicted an interaction between the isonicotinoyl moiety of the inhibitor and Tyr185. This hypothesis was supported by the fact that a higher 50% inhibitory concentration of the adduct was measured for MabA Y185L than for the wild-type enzyme, while both proteins presented similar affinities for NADP(+). The crystal structure of MabA Y185L that was solved showed that the substitution of Tyr185 induced no significant conformational change. The description of the first inhibitor of the beta-ketoacyl reduction step of fatty acid biosynthesis should help in the design of new antituberculous drugs efficient against multidrug-resistant tubercle bacilli.

ethA, inhA, and katG loci of ethionamide-resistant clinical Mycobacterium tuberculosis isolates

Ethionamide (ETH) is a structural analog of the antituberculosis drug isoniazid (INH). Both of these drugs target InhA, an enzyme involved in mycolic acid biosynthesis. INH requires catalase-peroxidase (KatG) activation, and mutations in katG are a major INH resistance mechanism. Recently an enzyme (EthA) capable of activating ETH has been identified. We sequenced the entire ethA structural gene of 41 ETH-resistant Mycobacterium tuberculosis isolates. We also sequenced two regions of inhA and all or part of katG. The MICs of ETH and INH were determined in order to associate the mutations identified with a resistance phenotype. Fifteen isolates were found to possess ethA mutations, for all of which the ETH MICs were > or =50 microg/ml. The ethA mutations were all different, previously unreported, and distributed throughout the gene. In eight of the isolates, a missense mutation in the inhA structural gene occurred. The ETH MICs for seven of the InhA mutants were > or =100 microg/ml, and these isolates were also resistant to > or =8 microg of INH per ml. Only a single point mutation in the inhA promoter was identified in 14 isolates. A katG mutation occurred in 15 isolates, for which the INH MICs for all but 1 were > or =32 microg/ml. As expected, we found no association between katG mutation and the level of ETH resistance. Mutations within the ethA and inhA structural genes were associated with relatively high levels of ETH resistance. Approximately 76% of isolates resistant to > or =50 microg of ETH per ml had such mutations.

Detection of a point mutation associated with high-level isoniazid resistance in Mycobacterium tuberculosis by using real-time PCR technology with 3'-minor groove binder-DNA probes

Tuberculosis remains one of the leading infectious causes of death worldwide. The emergence of drug-resistant strains of Mycobacterium tuberculosis is a serious public health threat. Resistance to isoniazid (INH) is the most prevalent form of resistance in M. tuberculosis and is mainly caused by mutations in the catalase peroxidase gene (katG). Among high-level INH-resistant isolates (MIC > or = 2), 89% are associated with a mutation at codon 315 of katG. There is a need to develop rapid diagnostic tests to permit appropriate antibiotic treatment and to improve clinical management. Therefore, a single-tube real-time PCR, using a novel kind of probe (3'-minor groove binder-DNA probe), was developed to detect either the wild-type or the mutant codon directly in Ziehl-Neelsen-positive sputum samples. The detection limit of the assay for purified DNA was 5 fg per well (one mycobacterial genome), and with spiked sputum samples, it was 20 copies per well, corresponding to 10(3) mycobacteria per ml of sputum. Sputum samples from 20 patients living in Kazakhstan or Moldova and infected with monodrug- or multidrug-resistant M. tuberculosis and 20 sputum samples from patients infected with INH-susceptible M. tuberculosis were tested. The sensitivities and specificities of the probes were 70 and 94% for the wild-type probe and 82 and 100% for the mutant probe. Binding to either probe was nonambiguous. This real-time PCR allows the rapid identification of a mutant katG allele and can easily be implemented in a clinical microbiology laboratory.

Overexpression of inhA, but not kasA, confers resistance to isoniazid and ethionamide in Mycobacterium smegmatis, M. bovis BCG and M. tuberculosis

The inhA and kasA genes of Mycobacterium tuberculosis have each been proposed to encode the primary target of the antibiotic isoniazid (INH). Previous studies investigating whether overexpressed inhA or kasA could confer resistance to INH yielded disparate results. In this work, multicopy plasmids expressing either inhA or kasA genes were transformed into M. smegmatis, M. bovis BCG and three different M. tuberculosis strains. The resulting transformants, as well as previously published M. tuberculosis strains with multicopy inhA or kasAB plasmids, were tested for their resistance to INH, ethionamide (ETH) or thiolactomycin (TLM). Mycobacteria containing inhA plasmids uniformly exhibited 20-fold or greater increased resistance to INH and 10-fold or greater increased resistance to ETH. In contrast, the kasA plasmid conferred no increased resistance to INH or ETH in any of the five strains, but it did confer resistance to thiolactomycin, a known KasA inhibitor. INH is known to increase the expression of kasA in INH-susceptible M. tuberculosis strains. Using molecular beacons, quantified inhA and kasA mRNA levels showed that increased inhA mRNA levels corre--lated with INH resistance, whereas kasA mRNA levels did not. In summary, analysis of strains harbouring inhA or kasA plasmids yielded the same conclusion: overexpressed inhA, but not kasA, confers INH and ETH resistance to M. smegmatis, M. bovis BCG and M. tuberculosis. Therefore, InhA is the primary target of action of INH and ETH in all three species.

The susceptibility of Mycobacterium tuberculosis to isoniazid and the Arg-->Leu mutation at codon 463 of katG are not associated

A mutation (CCG-->CTG [Arg-->Leu]) in codon 463 of katG (catalase peroxidase) of Mycobacterium tuberculosis has been found in isoniazid (INH)-resistant strains. A PCR restriction endonuclease analysis to detect this mutation was applied to 395 M. tuberculosis isolates from patients in The Netherlands. The proportion of isolates with a detectable mutation was 32% (32 out of 100) and 29% (85 out of 295) among INH-susceptible isolates and INH-resistant or -intermediate isolates, respectively. Sequencing of five INH-susceptible isolates with such mutations showed that all five had the Arg463Leu mutation. We conclude that the Arg463Leu mutation of katG of M. tuberculosis is not a reliable indicator of INH resistance.

Genomic mutations in the katG, inhA and aphC genes are useful for the prediction of isoniazid resistance in Mycobacterium tuberculosis isolates from Kwazulu Natal, South Africa

Genotypic analysis of isoniazid (INH) resistance in 79 isolates of M. tuberculosis (MTB) was undertaken by PCR-single strand conformation polymorphism (SSCP), Msp1 restriction enzyme analysis and sequence analysis of specific regions of three genes (part of the coding sequence of katG, and promoter regions of the inhA operon and ahpC) in order to determine the particular allelic variants within these genes. The epidemiologic relatedness was determined using IS6110 and polymorphic G-C region (PGRS (MTB484(1)) based restriction fragment length polymorphism (RFLP). Mutations in katG, inhA locus and ahpC were identified in 77/79, 19/79 and 10/79 isolates respectively. The ability of PCR-SSCP to detect mutations associated with INH resistance in katG, inhA and ahpC genes was 100% (CI 91.2-99.7%), 98.7% (CI 74.0-99.9%), and 100% (CI 69.2-100%) respectively. Specificity was 100%. All isolates with mutations in the 209 bp fragment of the MTB katG gene containing the Ser315Thr codon were positive by PCR-RFLP using Msp1 enzyme restriction analysis. Sixteen of 19 isolates with alterations on the 3' end of the ribosome binding site upstream of mabA in inhA locus simultaneously harbored Ser315Thr mutations in KatG. In 9/10 isolates, mutations in the ahpC promoter region were located in the 105 bp oxyR-ahpC intergenic region. None of 17 INH drug susceptible isolates harbored mutations in any of the three genetic regions, although the katG1 allele (Arg 463 Leu) was present in one isolate. Characterization by IS6110/PGRS(MTB484(1))RFLP analysis revealed that a number of drug resistant clones are widespread in the community. We conclude that the frequency of the Ser315Thr katG mutation in the local strain population makes the PCR-RFLP MTB katG assay a reliable, rapid and useful method for detecting INH resistance.

Inactivation of the inhA-encoded fatty acid synthase II (FASII) enoyl-acyl carrier protein reductase induces accumulation of the FASI end products and cell lysis of Mycobacterium smegmatis

The mechanism of action of isoniazid (INH), a first-line antituberculosis drug, is complex, as mutations in at least five different genes (katG, inhA, ahpC, kasA, and ndh) have been found to correlate with isoniazid resistance. Despite this complexity, a preponderance of evidence implicates inhA, which codes for an enoyl-acyl carrier protein reductase of the fatty acid synthase II (FASII), as the primary target of INH. However, INH treatment of Mycobacterium tuberculosis causes the accumulation of hexacosanoic acid (C(26:0)), a result unexpected for the blocking of an enoyl-reductase. To test whether inactivation of InhA is identical to INH treatment of mycobacteria, we isolated a temperature-sensitive mutation in the inhA gene of Mycobacterium smegmatis that rendered InhA inactive at 42 degrees C. Thermal inactivation of InhA in M. smegmatis resulted in the inhibition of mycolic acid biosynthesis, a decrease in hexadecanoic acid (C(16:0)) and a concomitant increase of tetracosanoic acid (C(24:0)) in a manner equivalent to that seen in INH-treated cells. Similarly, INH treatment of Mycobacterium bovis BCG caused an inhibition of mycolic acid biosynthesis, a decrease in C(16:0), and a concomitant accumulation of C(26:0). Moreover, the InhA-inactivated cells, like INH-treated cells, underwent a drastic morphological change, leading to cell lysis. These data show that InhA inactivation, alone, is sufficient to induce the accumulation of saturated fatty acids, cell wall alterations, and cell lysis and are consistent with InhA being a primary target of INH.

The genetics and biochemistry of isoniazid resistance in mycobacterium tuberculosis

Although the primary targets of activated isoniazid (INH) are proteins involved in the biosynthesis of cell wall mycolic acids, clinical resistance is dominated by specific point mutations in katG. Mutations associated with target mutations contribute to, but still cannot completely explain, resistance to INH. Despite the wealth of genetic information currently available, the molecular mechanism of cell death induced by INH remains elusive.

InhA, a target of the antituberculous drug isoniazid, is involved in a mycobacterial fatty acid elongation system, FAS-II

Most drug-resistant clinical isolates of the tubercle bacillus are resistant to isoniazid, a first-line antituberculous drug. This antibiotic was shown to act on Mycobacterium tuberculosis by inhibiting a 2-trans-enoyl-acyl carrier protein reductase, called InhA. However, the exact role played by InhA in mycobacteria remained unclear. A mycobacterial enzyme fraction containing InhA was isolated. It displays a long-chain fatty acid elongation activity with the characteristic properties described for the FAS-II (fatty acid synthetase II) system. Inhibition of this activity by InhA inhibitors, namely isoniazid, hexadecynoyl-CoA or octadecynoyl-CoA, showed that InhA belongs to the FAS-II system. Moreover, the InhA inhibitors also blocked the biosynthesis of mycolic acids, which are major lipids of the mycobacterial envelope. The data strongly suggest that isoniazid acts on the mycobacterial cell wall by preventing the FAS-II system from producing long-chain fatty acid precursors for mycolic acid biosynthesis.

Obesity associated with a mutation in a genetic regulator of adipocyte differentiation

BACKGROUND

There is increasing evidence of genetic factors leading to obesity, but the exact genes involved have not been defined. Peroxisome-proliferator-activated receptor gamma2 (PPARgamma2) is a transcription factor that has a key role in adipocyte differentiation, and therefore mutations of the gene for this factor might predispose people to obesity.

METHODS

We studied 358 unrelated German subjects, including 121 obese subjects (defined as those with a body-mass index [the weight in kilograms divided by the square of the height in meters] of more than 29). We evaluated these subjects for mutations in the gene for PPARgamma2 at or near a site of serine phosphorylation at position 114 that negatively regulates the transcriptional activity of the protein, using a polymerase-chain-reaction-based assay coupled with specific endonuclease digestion. The activity of the mutation identified was analyzed by retroviral transfection and overexpression in murine fibroblasts.

RESULTS

Four of the 121 obese subjects had a missense mutation in the gene for PPARgamma2 that resulted in the conversion of proline to glutamine at position 115, as compared with none of the 237 subjects of normal weight (P=0.01). All the subjects with the mutant allele were markedly obese, with body-mass-index values ranging from 37.9 to 47.3, as compared with a mean of 33.6 in the other obese subjects. Overexpression of the mutant gene in murine fibroblasts led to the production of a protein in which the phosphorylation of serine at position 114 was defective, as well as to accelerated differentiation of the cells into adipocytes and greater cellular accumulation of triglyceride than with the wild-type PPARgamma2. These effects were similar to those of an in vitro mutation created directly at the Ser114 phosphorylation site.

CONCLUSIONS

A Pro115Gln mutation in PPARgamma2 accelerates the differentiation of adipocytes and may cause obesity.

The mabA gene from the inhA operon of Mycobacterium tuberculosis encodes a 3-ketoacyl reductase that fails to confer isoniazid resistance

A target of the anti-tuberculosis drugs isoniazid (INH) and ethionamide (ETH) has been shown to be an enoyl reductase, encoded by the inhA gene. The mabA (mycolic acid biosynthesis A) gene is located immediately upstream of inhA in Mycobacterium tuberculosis, Mycobacterium bovis and Mycobacterium smegmatis. The MabA protein from M. tuberculosis was expressed in Escherichia coli and shown to have 3-ketoacyl reductase activity, consistent with a role in mycolic acid biosynthesis. In M. smegmatis, inhA and mabA are independently transcribed, but in M. tuberculosis and M. bovis BCG, mabA and inhA constitute a single operon. Several INH-ETH-resistant M. tuberculosis clinical isolates contain point mutations in the ribosome-binding site of mabA in the mabA-inhA operon. However, genetic dissection of this operon reveals that the INH-ETH-resistance phenotype is encoded only by inhA, and not by mabA.

Mechanisms of isoniazid resistance in Mycobacterium tuberculosis

Isoniazid (INH) is a widely used front-line antituberculous agent with bacteriocidal activity at concentrations as low as 150 nM against Mycobacterium tuberculosis. INH is a prodrug and requires activation by an endogenous mycobacterial enzyme, the catalase-peroxidase KatG, before exerting toxic effects on cellular targets. Resistance to INH develops primarily through failure to activate the prodrug due to point mutations in the katG gene. In addition to mutations in katG, mutations in several other loci, such as the alkylhydroperoxidase AhpC and the enoylreductase InhA, may contribute to INH resistance. Although these markers can be used to accurately predict clinical INH resistance in a large number of cases, the molecular mechanisms involved remain largely speculative and incomplete.

Deficiency of phosphofructo-1-kinase/muscle subtype in humans impairs insulin secretion and causes insulin resistance

Non-insulin-dependent diabetes mellitus (NIDDM) is caused by peripheral insulin resistance and impaired beta cell function. Phosphofructo-1-kinase (PFK1) is a rate-limiting enzyme in glycolysis, and its muscle subtype (PFK1-M) deficiency leads to the autosomal recessively inherited glycogenosis type VII Tarui's disease. It was evaluated whether PFK1-M deficiency leads to alterations in insulin action or secretion in humans. A core family of four members was evaluated for PFK1-M deficiency by DNA and enzyme-activity analyses. All members underwent oral and intravenous glucose tolerance tests (oGTT and ivGTT) and an insulin-sensitivity test (IST) using octreotide. Enzyme activity determinations in red blood cells showed that the father (46 yr, body mass index [BMI] 22. 4 kg/m2) and older son (19 yr, BMI 17.8 kg/m2) had a homozygous, while the mother (47 yr, BMI 28.4 kg/m2) and younger son (13 yr, BMI 16.5 kg/m2) had a heterozygous PFK1-M deficiency. DNA analyses revealed an exon 5 missense mutation causing missplicing of one allele in all four family members, and an exon 22 frameshift mutation of the other allele of the two homozygously affected individuals. The father showed impaired glucose tolerance, and the mother showed NIDDM. By ivGTT, both parents and the older son had decreased first-phase insulin secretion and a diminished glucose disappearance rate. The IST showed marked insulin resistance in both parents and the older, homozygous son, and moderate resistance in the younger son. PFK1-M deficiency causes impaired insulin secretion in response to glucose, demonstrating its participation in islet glucose metabolism, and peripheral insulin resistance. These combined metabolic sequelae of PFK-1 deficiency identify it as a candidate gene predisposing to NIDDM.

Genetics of drug resistance in tuberculosis

In the last few years, there has been considerable progress in our understanding of the mechanisms of action and resistance to antimycobacterials. To date, there is information about 11 genes involved in resistance in M. tuberculosis. This has prompted the development of novel tests for the rapid identification of resistant strains, and has provided invaluable insight into unique mycobacterial structures, which are important targets for the development of new inhibitory compounds.

Genotypic assessment of isoniazid and rifampin resistance in Mycobacterium tuberculosis: a blind study at reference laboratory level

Progress in understanding the basis of resistance to isoniazid (INH) and rifampin (RMP) has allowed molecular tests for the detection of drug-resistant tuberculosis to be developed. Consecutive isolates (n = 95) of Mycobacterium tuberculosis, from a Spanish reference laboratory investigating outbreaks of multidrug-resistant tuberculosis, were coded and sent to two external laboratories for genotypic analysis of INH and RMP resistance by PCR-single-strand conformation polymorphism (SSCP) analysis of specific regions of four genes: part of the coding sequence of katG and the promoter regions of inhA and ahpC for INH and the RMP resistance region of rpoB. After correction for the presence of outbreak strains and multiple isolates from single patients, RMP resistance was detected successfully by PCR-SSCP in > 96% of the RMP-resistant strains. PCR-SSCP had a sensitivity of 87% for INH resistance detection, and mutations in katG, inhA, katG-inhA, ahpC, and katG-ahpC were identified in 36.8, 31.6, 2.6, 13.2, and 2.6%, respectively, of the unique strains. Specificity was 100%. Molecular detection of resistance to the two main antituberculous drugs, INH and RMP, can be accomplished accurately by using a strategy which limits analysis to four genetic regions. This may allow the expedient analysis of drug resistance by reference laboratories.

Muscle phosphofructokinase deficiency in two generations

Phosphofructokinase (PFK) is the key regulatory enzyme of glycolysis. Patients lacking the muscular isoform of PFK typically present with myopathy and compensated hemolysis (glycogenosis type VII or Tarui's disease). Since 1965 about 30 cases of muscular PFK deficiency have been reported. In most cases family history suggests a recessive inherited trait. We describe a family of Ashkenazi Jewish origin with two members in subsequent generations suffering from muscular PFK deficiency. The propositus, a 19-year-old male patient presented with weakness, myalgias and exercise intolerance since early infancy. His father also had early fatigue on exercise with myalgias; the mother and a 12-year-old brother were asymptomatic. Muscle biopsy of both the propositus and his father showed increased glycogen storage and absent histochemical stain for PFK. Biochemical studies of muscle revealed a markedly decreased PFK activity and DNA analysis of the muscle PFK gene revealed compound heterozygosity in both cases. This is the first description of proven muscle PFK deficiency (glycogenosis type VII) in two subsequent generations.

katG mutations in isoniazid-resistant Mycobacterium tuberculosis isolates recovered from Finnish patients

katG and inhA genes from isoniazid-resistant Mycobacterium tuberculosis strains isolated in Finland were examined by PCR or sequencing. By PCR, katG was not detected in 3 of 54 strains. Sequencing of katG from 13 strains showed small point mutations or insertions; a previously described mutation causing a Ser-to-Thr change at position 315 was found in 4 strains, and there were nine new missense mutations of katG. A 209-bp segment of inhA from 17 strains was sequenced, but no mutations were observed. This result indicates that different mutations prevail in different geographical areas.